HCMV is a ubiquitous herpesvirus which has the ability to establish a lifelong latent infection. Reactivation of latent virus is frequently observed in recipients of solid organs and bone marrow transplants and is a significant cause of morbidity and mortality in newborns and in immunocompromised hosts. Latency is operationally defined as the inability to detect infectious virus despite the presence of viral DNA. However, the molecular mechanisms by which CMV establishes a latent infection and reactivates from latency are not well understood. Because of the lack of animal models to study HCMV infection in vivo, we and others have used MCMV as a model to study CMV latency and reactivation. We have developed a transplant model for transcriptional reactivation of IE gene expression. On the basis of these studies, we have hypothesized that CMV establishes a true latent infection in which genes associated with productive infection, including the IE genes, are not expressed, and that transcriptional reactivation is due to activation of signaling pathways which lead to binding of transcription factors to their cognate sites in the enhancer. Here we hypothesize that transcriptional silencing in latent infection is due to interaction of the major immediate early promoter (MIEP) with proteins which maintain the chromatin in a condensed and transcriptionally inactive state. The virus would be able to persist in this state because latently infected cells would be invisible to the host immune response. We further hypothesize that transcriptional reactivation is induced by inflammatory stimuli which result in changes in the histones associated with the MIEP such that they acquire modifications associated with transcriptionally active chromatin. These modifications lead to opening of the chromatin which allows transcription factors such as NFkB access to the MIEP. We hypothesize that transcriptional reactivation of IE gene expression is accompanied both by chromatin remodeling and by binding of NFkB to the MIEP. We propose to test this hypothesis by using chromatin immunoprecipitation assays to characterize coactivators, transcription factors, transcriptional repressors and modification of histones associated with the MIEP during acute and latent infection and after reactivation induced by transplantation. These studies will form the basis for a future R01 investigating mechanisms by which chromatin remodeling proteins are recruited to the MIEP. These studies will advance our understanding of the mechanisms of CMV latency and reactivation and may lead to development of new therapies to prevent CMV disease. [unreadable] [unreadable] PUBLIC HEALTH RELEVANCE: Cytomegalovirus (CMV) is a ubiquitous herpesvirus which establishes a lifelong latent infection in which the viral DNA is present, but no virus is produced. Primary infection with CMV during pregnancy can cause death or serious neurological complications in the fetus. Reactivation of latent virus can cause significant morbidity or mortality in immunocompromised patients. The goal of this proposal is to understand the molecular mechanisms by which the virus establishes latent infection and the molecular pathways that trigger reactivation of latent virus. These studies will advance our understanding of the mechanisms of CMV latency and reactivation and may lead to development of new therapies to prevent CMV disease. [unreadable] [unreadable] [unreadable]